Method and system for determining position and orientation of a measuring instrument

ABSTRACT

A method for determining position and orientation of a first measuring instrument is disclosed. A second MI and at least one reflective target including a retroreflector unit are arranged in the vicinity of the first MI. At least one imaging module is arranged in the first MI for determining orientation thereof. The at least one imaging module in the first MI can be used in a similar manner as a tracker unit of an optical total station, by way of detecting optical radiation emitted from the second MI and reflected by the at least one TGT.

TECHNICAL FIELD

The present invention relates to the field of measuring, in particularsurveying. In particular, the present invention is related to a methodand a system for determining position and orientation of a firstmeasuring instrument, such as a portable scanner allowing for hand-heldoperation by a user.

BACKGROUND

The art of surveying involves determination of unknown positions,surfaces or volumes of objects using measurements of angles anddistances. In order to make these measurements, a surveying instrumentfrequently comprises an electronic distance measuring device (EDM) thatmay be integrated in a so-called total station. A distance measuringtotal station combines electronic, optical and computer techniques andis furthermore provided with a computer or control unit with writableinformation for controlling the measurements to be performed and forstoring data obtained during the measurements. Preferably, the totalstation calculates the position of a target in a fixed ground-basedcoordinate system. In, for example, WO 2004/057269 by the sameapplicant, such a total station is described in more detail.

A tracker system or unit of an optical total station normally focuses alight signal from a target located at an object, either a reflection ofan incident measuring beam comprising optical radiation from the targetor from an active device on the target, onto a detector. A servo systemof the total station may move or turn the total station based on thesignal from the detector.

Further, when performing distance measuring or surveying tasks using adistance measuring total station at a work site, it is often desirableto measure a surface or volume of an object being present on the worksite. In such a work site, it may, for example, be desirable to scan asurface of an object, for example, a wall of a building to obtain animage of the wall. For such applications, a distance measuring totalstation may be implemented as a geodetic scanner for determining theappearance of the object or target based on the measurements ofdistances to positions of interest at the surface of the target. Such ascanner may register the surface or volume of the target or even monitorchanges in a scene.

The geodetic scanner is often set up at a certain position at the worksite, from which position the surface or volume of the target that is tobe scanned is visible. For scanning surfaces or volumes of the target orof another target that are not visible from the position at which thegeodetic scanner is set up, the geodetic scanner has to be moved toanother position at which visibility of the surfaces or volumes desiredto be scanned is attained. This process may be cumbersome andtime-consuming, e.g., due to the labor involved in moving the geodeticscanner and in setting up the geodetic scanner once it has beenpositioned at a new position.

For overcoming these disadvantages, mobile scanners are available thatcan be operated hand-held. In other words, a user can carry the mobilescanner to a suitable position at which the surfaces or volumes desiredto be scanned are visible, and at that position operate the scanner soas to perform scanning of the surfaces or volumes. In order to knowwhere the light beam of the mobile scanner is aiming during ameasurement session, e.g., in relation to some fixed coordinate systemsuch as a coordinate system related to another measuring instrument atthe work site, position and orientation of the mobile scanner must bemonitored during the measurement session, e.g., in relation to the fixedcoordinate system.

EP 1200853 A1 discloses a method for determining the orientation of anobject onto which a reflector is arranged, which reflector has anon-adjustable or adjustable orientation with respect to the object. Alaser tracker is sending out a laser beam impinging on the reflector.The direction and path length of the laser beam and the angle ofincidence of the laser beam into the reflector and/or the reflectororientation relative to the object are measured. Using the measureddata, the orientation and position of the object are determined. Formeasuring the angle of incidence, a position sensitive diode positionsensor, arranged in a plane perpendicular to the optical axis of thereflector, is arranged behind the reflector such that the beam partpenetrating through the reflector impinges thereon. According to EP1200853 A1, the position of the light spot detected by the sensor isdirectly dependent on the angle of incidence of the laser beam into thereflector.

U.S. Pat. No. 7,312,862 B2 discloses a measurement system fordetermining six degrees of freedom of a reflector or of an object onwhich the reflector is arranged. The measurement system comprises alaser tracker equipped with a distance measuring apparatus, the lasertracker directing a laser beam (measurement beam) to the reflector andfollowing or tracking the reflector, when moving, and detecting thedirection of the measurement beam relatively to the tracker. Themeasurement system also comprises an optically detectable additionelement arranged on the object for determining rotation of the reflectoror of the object about the reflector axis or about the measurement beam.The addition element consists of two light points, which are passivemarkings, reflectors, active light sources or points produced by lightbeams directed against the object. The two light points are imaged in animaging plane with a camera that is stationary with respect to themeasurement beam during measurement. Each of the light points isidentified in an image taken by the camera, or the light points aresynchronized with the camera, such that the light points appear oneafter the other on consecutively recorded images, and a line connectingthe two light points is determined from the images. According to U.S.Pat. No. 7,312,862 B2, an angle between the line and a likewise directedreference line is a measure of the roll angle of the reflector or theobject.

Such arrangements for determining orientation of an object may provideonly limited angular accuracy and/or angular resolution that can beinsufficient in some applications. In other words, such arrangements fordetermining orientation of an object may not be able to determineorientation of the object with the required degree of accuracy.

Such arrangements for determining orientation of an object may provideonly a limited range of operation with regards to the distance betweenthe object and the measuring apparatus effectuating the determination oforientation of the object with regards to some applications. That is,the maximum distance between the object and the measuring apparatuseffectuating the determination of orientation of the object may berelative small.

SUMMARY

It is with respect to the above considerations and others that thepresent invention has been made. The present invention seeks tomitigate, alleviate or eliminate one or more of the above-mentioneddeficiencies and disadvantages singly or in combination. In particular,it would be desirable to achieve a method for determining position andorientation of a first measuring instrument, which method is capable ofdetermining orientation of the object with a high degree of accuracywith regards to angle of rotation about one or more rotational axes. Itwould also be desirable to achieve a method for determining position andorientation of a first measuring instrument, which method provides along range of operation with regards to the distance between the firstmeasuring instrument and the measuring apparatus responsible for makingthe determination.

To achieve this, a method and a system having the features as defined inthe independent claims are provided. Further advantageous embodiments ofthe present invention are defined in the dependent claims.

In order to clarify, the wording “total station” used herein refers to adistance measuring instrument with an integrated distance and angularmeasurement, i.e. with combined electronic, optical and computertechniques. Such an instrument can provide both the distance as well asthe vertical and horizontal direction towards a target, whereby thedistance is measured against an object or target such as a reflector.The wording “total station” as used herein includes the following terms:survey unit, geodetic instrument.

According to a first aspect of the present invention, there is provideda method for determining position and orientation of a first measuringinstrument (MI), wherein a second MI and at least one target (TGT)preferably are located in the vicinity of the first MI. The first MIcomprises a retroreflector unit, at least one first optical radiationsource configured to emit optical radiation when activated, and at leastone imaging module. The second MI comprises at least one first opticalradiation source configured to emit optical radiation when activated.The at least one TGT comprises identification means enabling anidentification of the TGT in an image.

The method comprises measuring angle and distance to the first MI andthe at least one TGT, respectively, in relation to the second MI.

The at least one imaging module is caused to capture images, includingalternating activation and deactivation of the at least one secondoptical radiation source.

An image representation of each captured image is produced.

Differential images using the image representations are created.

Information regarding objects being present in the differential imagesare extracted.

Using the extracted information, the second MI and the at least one TGT,respectively, are distinguished from any other objects present in theimages.

On a condition that the second MI and the at least one TGT can bedistinguished from any other objects present in the images, and on basisof the extracted information, any of the image representations is/areprocessed to determine angular information of the second MI and/or theat least one TGT with respect to at least one axis, respectively.

On a condition that the second MI and the at least one TGT can bedistinguished from any other objects present in the images, and on basisof angle and distance to the second MI and/or the at least one TGT,respectively, in relation to the first MI, and the angular information,orientation of the first MI is estimated.

According to a second aspect of the present invention, there is provideda system comprising a first MI, a second MI and at least one TGT, eachof the second MI and the at least one TGT preferably being located inthe vicinity of the first MI. The first MI comprises a retroreflectorunit. The TGT comprises an identifying means enabling the TGT to beidentified in an image capturing the TGT.

The second MI comprises at least one second optical radiation source,configured to emit optical radiation when activated, and a positioncalculating circuit, comprising an angle measuring system and a distancemeasuring system, adapted to measure angle and distance to the first MIand the at least one TGT, respectively.

The first MI comprises at least one first optical radiation sourceconfigured to emit optical radiation when activated, a control moduleand a communication module adapted to, on instruction from the controlmodule, communicate control signals to the second MI for activating ordeactivating the at least one second optical radiation source.

The communication module is adapted to receive signals from the secondMI indicating distances and angles determined by the second MI.

The first MI comprises at least one imaging module adapted to, oninstruction from the control module, capture an image, wherein thecontrol module is adapted to cause the at least one imaging module tocapture images including alternating activation and deactivation of theat least one first optical radiation source and the at least one secondoptical radiation source, and produce an image representation of eachcaptured image.

The first MI comprises a processing module adapted to createdifferential images using the image representations, extract informationregarding objects being present in the differential images, anddistinguish the second MI and the at least one TGT, respectively, fromany other objects present in the images using the extracted information.

The processing module is adapted to, on a condition that the second MIand the at least one TGT can be distinguished from any other objectspresent in the images, on basis of the extracted information, processany of the image representations to determine angular information of thesecond MI and/or the at least one TGT with respect to at least one axis,respectively.

The processing module is adapted to, on a condition that the second MIand the at least one TGT can be distinguished from any other objectspresent in the images, on basis of angle and distance to the second MIand the at least one TGT, respectively, and the angular information,estimate orientation of the first MI.

Thus, the present invention is based on utilizing one or several cameradevices, or imaging modules, arranged in the first MI for determiningorientation thereof. The at least one imaging module in the first MI canbe used to detect the identifying means of the TGT and can be used in asimilar manner as a tracker unit of an optical total station, by meansof detecting optical radiation emitted from the second MI.

Optionally or alternatively, orientation of the first MI may beestimated on basis of measured or estimated physical coordinates of thefirst MI and the at least one TGT established by the second MI andcommunicated to the processing module, e.g., by means of wirelesscommunication link.

The orientation and/or position of the first MI can be determined withrespect to a coordinate system suitable for the particular situation orapplication. For example, the orientation and/or position of the firstMI can be determined with respect to a coordinate system fixed on thesecond MI.

The first MI may for example comprise a portable scanner configured suchas to enable hand-held operation by a user (in the following such aportable scanner may be referred to as “hand-held unit” or “hand-heldscanner”). The portable scanner can for example be utilized fordetermining the appearance of an object or target.

The position of the first MI is determined or monitored by the secondMI, which second MI for example may comprise a surveying instrument suchas a total station or theodolite, while orientation of the first MI isdetermined or monitored by the first MI itself.

For enabling determination of orientation of a hand-held unit, accordingto one example a camera device in a MI such as a total station can bearranged to determine or monitor an array of diodes arranged on thehand-held unit. Compared to such a solution, by a method or systemaccording to the first and second aspect of the invention, respectively,an increased angular accuracy/angular resolution may be achieved. Thisis due to possibility of a finer spacing of pixels in images captured bythe imaging module compared to the spacing of ‘pixels’, i.e. diodes, inthe array on the hand-held unit.

Compared to an arrangement where an array of diodes arranged on thefirst MI is monitored by a camera device arranged on the second MI inorder to determine orientation of the first MI, an arrangement based onthe at least one imaging module in the first MI being used for detectingoptical radiation emitted from the second MI and the at least one TGT,which in turn allows for estimating orientation of the first MI, mayachieve a relatively long range of operation with regards to thedistance between the first MI and the second MI.

By a method or system according to the first and second aspect of theinvention, respectively, an increased flexibility with regards to tuningor adjusting angular accuracy/angular resolution of the determinedorientation of the first MI may be achieved. This can for example beaccomplished by selecting an imaging device to be arranged in the firstMI having a pre-selected resolution/pixel density by which a desiredangular accuracy/angular resolution of the determined orientation of thefirst MI may be provided.

By a method or system according to the first and second aspect of theinvention, respectively, an increased speed in scanning an object ortarget may be achieved. This is due to the configuration of the systemthat enables the first MI to be portable. In this case, the first MI canbe operated from various positions at a work site without the need ofhaving to go through a time-consuming process of setting up a geodeticscanner at each of the desired operating positions at the work site.

By the possibility of the first MI being portable, areas or surfacesdesired to be scanned can be reached by optical radiation emitted fromthe first MI by the user positioning the first MI appropriately, even ifthose areas or surfaces are hidden from view from a fixed position atthe work site.

As discussed above, the angular information of the second MI and/or theat least one TGT can be determined by any of the image representationsbeing processed on basis of the extracted information regarding objectsbeing present in the differential images. For example, the angularinformation of the second MI and/or the at least one TGT can bedetermined with respect to a coordinate system related to the at leastone imaging module or device.

However, a coordinate transformation may be performed in order totransform any angular information, e.g., orientation (or angles),determined with respect to some coordinate system, to another coordinatesystem suitable for the particular situation or application. Suchcoordinate transformations are known in the art.

In the context of the present application, by angular accuracy of anarrangement for determining orientation of an object, it is meant thedegree of accuracy with regards to angle of rotation about one or morerotational axes that can be achieved, i.e. the numerical accuracy withwhich the orientation or angle can be determined.

In the context of the present application, by angular resolution of anarrangement for determining orientation of an object, it is meant arelatively small angle or even the smallest angle that can be determinedwhen the object undergoes a (small) change in orientation.

According to a third aspect of the present invention, there is provideda first MI for scanning a surface or volume of an object to determineappearance of the object, which first MI may be used a system accordingto the second aspect of the present invention or any embodiment thereof.The first MI is adapted to transmit optical radiation from the at leastone first optical radiation source to and receive optical radiationreflected from a position on the object, in order to measure angle anddistance to the position on the object, wherein the direction of thetransmitted optical radiation and/or the received optical radiation ismonitored by consecutively determining position and orientation of thefirst MI.

The first MI may comprise a scanning device configured to guide thetransmitted optical radiation at predetermined positions over theobject.

According to a fourth aspect of the present invention, there is provideda method for scanning a surface or a volume of an object to determineappearance of the object with a first MI, which first MI comprises atleast one first optical radiation source configured to emit opticalradiation when activated.

The method comprises transmitting optical radiation from the at leastone first optical radiation source to and receiving optical radiationreflected from a position on the object in order to measure angle anddistance to the position on the object.

The direction of the transmitted optical radiation and/or the receivedoptical radiation is monitored by determining position and orientationof the first MI by consecutively performing a method according to thefirst aspect of the present invention or any embodiment thereof.

The transmitted optical radiation may be guided at predeterminedpositions over the object.

According to a fifth aspect of the present invention, there is provideda first MI configured such as to enable operation thereof in a systemaccording to the second aspect of the present invention or anyembodiment thereof.

According to a sixth aspect of the present invention, there is provideda computer program product comprising computer-executable components forperforming a method according to the first and/or fourth aspect of thepresent invention or any embodiment thereof when the computer-executablecomponents are executed on a processing unit.

According to a seventh aspect of the present invention, there isprovided a computer-readable digital storage medium comprising acomputer program product comprising computer-executable componentsadapted to, when executed on a processing unit, perform a methodaccording to the first and/or fourth aspect of the present invention orany embodiment thereof.

The present invention can be implemented in a computer program productthat, when executed in a processing unit, performs a method inaccordance with the present invention in an MI. The computer programproduct may, for example, be downloaded into the MI as an upgrade. Amethod in accordance with the present invention can be implemented foran MI using software, hardware, firmware or any combination thereof, asdesired or required in view of the particular circumstances orapplication.

In an embodiment of the present invention, the control module of thefirst MI is adapted to cause the at least one imaging module to captureimages including alternating activation and deactivation of the at leastone first optical radiation source and the at least one second opticalradiation source.

According to embodiments of the present invention, the identifying meansis a retroreflector unit and the TGT is a reflective target.

According to embodiments of the present invention, the identifying meanscomprises at least one optical radiation source configured tocontinuously emit optical radiation or to emit optical radiation whenactivated. The identification means may be at least one lamp, lightemitting diode, or similar light emitting device. If there is more thanone light emitting device, the devices can be arranged in a pattern. Thelight emitting device may emit fixed light, or blinking or flashinglight, which may be random, or in accordance with a predeterminedpattern. The light emitting device may be controlled by the first andsecond MI via, for example, a wireless communication link. Thereby, theat least one light emitting device can be controlled to blink or flashat receipt of an activation signal. Further, the at least one lightemitting device may emit light with a certain colour, and if there aremore than one light emitting device the device may emit light withdifferent colours.

According to embodiments of the present invention, the identifying meanscomprises a geometrical symbol or pattern, for example, one or morecircular surfaces, one or more square-shaped surfaces, one or morerhombical-shaped surfaces, or an arbitrary combination of such surfaces.The surface (-s) may be reflective and/or may include light emittingdevices.

With regards to creating differential images, the at least one imagingmodule may be adapted to capture images under different operatingconditions of at least the first MI and/or the second MI. Images may becaptured at different points in time. Differential images may beproduced based on the captured images, such as described in thefollowing.

According to a first configuration, at least one first image is capturedwhen the at least one second optical radiation source is activated andthe at least one first optical radiation source is deactivated. At leastone second image may be captured when the at least one second opticalradiation source is deactivated and the at least one first opticalradiation source is activated. At least one third image is captured whenboth of the at least one second optical radiation source and the atleast one first optical radiation source are deactivated.

According to a second configuration, at least one first image iscaptured when the at least one second optical radiation source isactivated and the at least one first optical radiation source isdeactivated. At least one second image may be captured when the at leastone second optical radiation source is activated and the at least onefirst optical radiation source is activated. At least one third imagemay be captured when the at least one second optical radiation sourceand the at least one first optical radiation source are deactivated.

According to a further configuration, if the identifying means is alight emitting device controlled by the first MI via wirelesscommunication, at least one first image can be captured when the atleast one second optical radiation source is activated and the at leastone optical radiation source of the TGT is deactivated. At least onesecond image may be captured when the at least one second opticalradiation source is deactivated and the at least one optical radiationsource of the TGT is activated. At least one third image can be capturedwhen both of the at least one second optical radiation source and the atleast one optical radiation source of TGT are deactivated.

With regards to creating differential images using the imagerepresentations, at least one first differential image between the atleast one first image representation and the at least one third imagerepresentation may be created. At least one second differential imagebetween the at least one second image representation and the at leastone third image representation may be created.

Information regarding objects being present in the differential imagesmay be extracted by extracting information regarding objects beingpresent in the at least one first differential image and the at leastone second differential image, respectively.

According to a another configuration, at least one first image iscaptured when the at least one second optical radiation source isactivated and the at least one first optical radiation source isdeactivated, and at least one second image is captured when the at leastone second optical radiation source is deactivated and the at least onefirst optical radiation source is activated.

With respect to the this configuration, at least one first differentialimage between the at least one first and the at least one second imagerepresentation may be created. In the at least one first differentialimage, intensity from the at least one second optical radiation sourceand intensity from the at least one first optical radiation source,which intensity arises from optical radiation reflected at the at leastone TGT, may have different sign. For example, in the at least one firstdifferential image, intensity from the at least one second opticalradiation source may be positive and intensity from the at least onefirst optical radiation source may be negative.

Further with respect to this configuration, information regardingobjects being present in the differential images may be extracted byextracting information regarding objects being present in the at leastone first differential image.

With regards to determining angular information of the second MI and theat least one TGT with respect to at least one axis, any of the imagerepresentations may be processed to estimate at least one angle betweenthe second MI and the at least one TGT with respect to the at least oneaxis. In this regard, the angular information may comprise the estimatedat least one angle.

The estimation of at least one angle between the second MI and the atleast one TGT with respect to the at least one axis may comprisedetermining distance between the second MI and the at least one TGT,distance between the second MI and the at least one axis and/or distancebetween the at least one TGT and the at least one axis.

Any one of the distance determinations may comprise determining a numberof pixels in any of the images between the second MI and the at leastone TGT, between the second MI and the at least one axis and/or betweenthe at least one TGT and the at least one axis, respectively. In thisregard, a dimension of a pixel in the images may correspond to apredetermined distance.

Distance between the first MI and the at least one TGT may be determinedin at least two ways, of which two examples are described in thefollowing.

According to a first example, the position of the first MI and theposition of the at least one TGT may be determined on basis of measuredangle and distance relatively to the first MI and the at least one TGT,respectively.

The distance between the first MI and the at least one TGT may then bedetermined on basis of the position of the first MI and the position ofthe at least one TGT.

According to a second example, distance between the first MI and the atleast one TGT may be derived from the above-mentioned extractedinformation.

A comparison between distances between the first MI and the at least oneTGT as determined in different ways may then be carried out.

On basis of the comparison, accuracy of the distinguishing of the MI andthe at least one TGT, respectively, from any other objects present inthe images may be assessed.

In other words, discrepancies between the distances between the first MIand the at least one TGT as determined in different ways may be checked.A large discrepancy, e.g., exceeding a predetermined threshold value,may then for example be used to reject the current measuring session.

In this manner, a procedure reducing or even eliminating false readings,i.e. inaccurately and/or incorrectly recognized targets and/or MIs, maybe achieved.

Measuring angle and distance to the first MI and the at least one TGT,respectively, in relation to the second MI may comprise transmittingoptical radiation from the at least one second optical radiation sourceand receiving optical radiation reflected by the retroreflector unit ofthe first MI and the retroreflector unit of the at least one TGT,respectively.

In this regard, time-of-flight of optical radiation from the at leastone second optical radiation source to the first MI and the at least oneTGT, respectively, may be measured.

Alternatively or optionally, phase difference of modulatedcontinuous-wave optical radiation from the at least one second opticalradiation source subsequent to the modulated continuous-wave opticalradiation having been reflected by the retroreflector unit of the firstMI and the retroreflector unit of the at least one TGT, respectively,may be measured.

The second MI may comprise a tracker and a servo system.

The tracker and servo system may be configured to monitor the positionof the first MI.

In this regard, sets of images including alternating activation anddeactivation of the at least one first optical radiation source and theat least one second optical radiation source may be consecutivelycaptured. Orientation of the first MI on basis of each of the capturedsets of images may be estimated.

In this manner, orientation of the first MI may be monitored, e.g. whilethe first MI is moving.

The communication module may be adapted to, on instruction from thecontrol module, communicate control signals to the second MI configuredto temporally synchronize the monitoring of the position of the first MIand the estimation of orientation of the first MI.

In a case where the second MI comprises a tracker and servo system, thesecond MI may not require a separate second optical radiation source asdescribed in the foregoing. Instead, an optical radiation sourcecomprised in the tracker and servo system may be utilized in place of asecond optical radiation source for providing similar or the samefunctionality as the second optical radiation source as described in theforegoing and in the following. Thus, the second optical radiationsource may be a part of the tracker and servo system.

The steps of any method disclosed herein do not have to be performed inthe exact order disclosed, unless explicitly stated.

The present invention relates to all possible combinations of featuresrecited in the claims.

Further objects and advantages of the various embodiments of the presentinvention will be described below by means of exemplifying embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments of the invention will be described below withreference to the accompanying drawings, in which:

FIG. 1 a is a schematic view of a system according to an exemplifyingembodiment of the present invention;

FIG. 1 b is a schematic block diagram of a system according to anexemplifying embodiment of the present invention;

FIGS. 2 a-2 c are examples of captured images for use in a methodaccording to an exemplifying embodiment of the present invention;

FIG. 3 is an example of a captured image for illustrating a principle ofa method according to an exemplifying embodiment of the presentinvention;

FIG. 4 is a schematic view of computer-readable storage mediumsaccording to exemplifying embodiments of the present invention; and

FIGS. 5 a-5 c are schematic flowcharts illustrating methods according toexemplifying embodiments of the present invention.

In the accompanying drawings, the same reference numerals denote thesame or similar elements throughout the views.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplifyingembodiments of the invention are shown. This invention may however beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided by way of example so that this disclosure will convey the scopeof the invention to those skilled in the art. Furthermore, like numbersrefer to like or similar elements throughout.

A total station is a distance measuring instrument with an integrateddistance and angular measurement, i.e. with combined electronic, opticaland computer techniques. Such a total station can provide both thedistance as well as the vertical and horizontal direction towards anobject or a target, whereby the distance is measured against areflecting surface or a reflector, e.g. a retroreflector of the cornercube type. A total station is further provided with a computer orcontrol unit with writable information for measurements to be performedand for storing data obtained during the measurements. The total stationmay calculate the position of a target in a fixed ground-basedcoordinate system. In, for example, WO 2004/057269 by the sameapplicant, such a total station is described in more detail.

Referring now to FIG. 1 a, there is shown a schematic view of a system100 according to an exemplifying embodiment of the present invention.

The system 100 comprises a first MI 110, a second MI 120 and tworeflective TGTs 130.

The number of TGTs in the system 100 is not limited to two, but thesystem 100 may comprise any suitable number of TGTs depending on theparticular situation and/or application, e.g., one TGT or three, four,five, six or more TGTs.

By utilizing several TGTs within the field of view of the imaging module(not shown in FIG. 1 a, see FIG. 1 b) of the first MI 110, the area ofoperation can be increased. For example, the area over which the firstMI 110 can be used, e.g., for scanning a surface or a volume of anobject to determine appearance of the object, can be increased byutilization of several TGTs appropriately placed in the vicinity of thefirst MI and/or the second MI.

The components of the system 100 will be described in more detail withreference to FIG. 1 b, in which there is shown a schematic block diagramof a system 100 according to an exemplifying embodiment of the presentinvention.

The system 100 comprises a first MI 110, a second MI 120 and areflective TGT 130. As indicated in FIG. 1 a, each of the second MI 120and the TGT 130 is arranged in the vicinity of the first MI 110. Each ofthe first MI 110 and the TGT 130 comprises a retroreflector unit 135.The system 100 is configured to determine position and orientation ofthe first MI 110, as discussed in further detail in the following withreference to the schematic flowcharts in FIGS. 5 a-5 c illustratingexemplifying embodiments of the present invention.

With further reference to FIG. 1 b, the second MI 120 comprises a secondoptical radiation source 121 configured to emit optical radiation whenactivated.

The second MI 120 comprises a position calculating circuit 122, whichcomprises an angle measuring system 124 and a distance measuring system126 adapted to measure angle and distance to the first MI 110 and theTGT 130, respectively.

The second MI 120 may for example comprise a total station such asdescribed in the foregoing, which total station is capable of providingboth the distance as well as the vertical and horizontal directiontowards an object or a target.

Angle and distance to the first MI 110 and the TGT 130, respectively,may be measured by the second MI 120 prior to or at the start of theprocedure of determining position and orientation of the first MI 110and/or at a number of successive points in time during the procedure ofdetermining position and orientation of the first MI 110.

In general, the TGT 130 is fixed at a site, while the first MI 110 maybe moveable. In this regard, the first MI may for example comprise aportable scanner configured such as to enable hand-held operation by auser. The scanner may be configured to determine the appearance of anobject.

Thus, according to one example, measurement of angle and/or distance tothe TGT 130 may be performed less frequently during, e.g., the procedureof determining position and orientation of the first MI 110, compared tomeasurement of angle and/or distance to the first MI 110. The lattermeasurement may be performed at predefined points in time during theprocess of determining position and orientation of the first MI 110,thereby continually updating measured angle and/or distance values forthe first MI 110.

The first MI 110 comprises at least one first optical radiation source111 configured to emit optical radiation when activated, and a controlmodule 113 adapted to selectively activate and deactivate the firstoptical radiation source 111.

The first MI 110 comprises a communication module 114. The communicationmodule 114 is adapted to, on instruction from the control module 113,communicate control signals to the second MI 120 for activating ordeactivating the second optical radiation source 121, e.g., via awireless communication link. Optionally, signals other than controlsignals may be communicated to the second MI 120 by means of thecommunication module 114. The communication module 114 may optionally beadapted to receive control signals or any other signals from the secondMI 120 and/or any other device capable of communicating signals.Communication to or from the communication module 114 may for example beperformed via a wireless communication link.

The communication module 114 is adapted to receive signals from thesecond MI 120 indicating distances and angles determined by the secondMI 120.

The first MI 110 comprises an imaging module 115. The imaging module 115is adapted to, on instruction from the control module 113, capture animage. The control module 113 is adapted to cause the imaging module 115to capture images, including alternating activation and deactivation ofthe first optical radiation source 111 and the second optical radiationsource 121, and produce an image representation of each captured image.

The first MI 110 comprises a processing module 116.

The processing module 116 is adapted to create differential images usingthe image representations, extract information regarding objects beingpresent in the differential images, and distinguish the second MI 120and the TGT 130, respectively, from any other objects present in theimages using the extracted information.

On a condition that the second MI 120 and the TGT 130 can bedistinguished from any other objects present in the images, theprocessing module 116, on basis of the extracted information, processesany of the image representations to determine angular information of thesecond MI 120 and/or the TGT 130 with respect to at least one axis,respectively. On basis of angle and distance to the second MI 120 andthe TGT 130, respectively, and the angular information, orientation ofthe first MI 110 is determined.

The second MI 120 may comprise a communication module (not shown in FIG.1 b) adapted to communicate signals, e.g., measured data, controlsignals, etc., to or receive signals from the first MI 110 and/or anyother device capable of communicating signals. The communication may forexample be performed via a wireless communication link.

Referring now to FIGS. 2 a-2 c, there are shown schematic views ofcaptured images, which in accordance with an exemplifying embodiment ofthe present invention may be used in creating differential images.

At least one first image is captured when the second optical radiationsource 121 is activated, and the first optical radiation source 111 isdeactivated. As indicated by the solid black circle in FIG. 2 a, a spotarising from optical radiation emitted by the second optical radiationsource 121 will be present in the first image.

At least one second image is captured when the second optical radiationsource 121 is deactivated, and the first optical radiation source 111 isactivated. As indicated by the solid black circle in FIG. 2 b, a spotarising from optical radiation emitted by the first optical radiationsource 111 and incident on the retroreflector unit 135 of the TGT 130will be present in the second image.

At least one third image is captured when both of the second opticalradiation source 121 and the first optical radiation source 111 aredeactivated, shown in FIG. 2 c.

After having produced image representations of each captured image,creating differential images may comprise creating at least one firstdifferential image between the at least one first and the at least onethird image representation, and creating at least one seconddifferential image between the at least one second and the at least onethird image representation.

Alternatively or optionally, differential images may be createdaccording to schemes other than the one described immediately above,such as have been discussed in the foregoing.

Referring now to FIG. 3, there is shown a schematic view of a capturedimage in accordance with an exemplifying embodiment of the presentinvention, wherein a second MI 120 and a reflective TGT 130 are visible.An image representation of the captured image may be processed such asto to determine angular information of the second MI 120 and the TGT 130with respect to at least one axis.

For example, distance B between the second MI 120 and an axis 152 and/ordistance A between the second MI 120 and an axis 150 may be determined.The axis 150 may for example coincide with an internal horizontal axisof the imaging module of the first MI (not shown in FIG. 3). The axis152 may for example coincide with an internal vertical axis of theimaging module of the first MI. Determination of distances may comprisedetermining a number of pixels in the captured image between the secondMI 120 and the axis 152 and the number of pixels between the second MI120 and the axis 150, respectively, wherein a dimension of a pixel inthe image corresponds to a predetermined distance.

For example, on basis of the distances A and B and/or possibly otherdistances deduced from processing of the captured image the angle Cshown in FIG. 3 may be determined.

It is noted that the orientations of the second MI 120 and the TGT 130shown in FIG. 3 with respect to the imaging module of the first MI arein accordance with a specific example.

The second MI 120 and the TGT 130, respectively, may exhibit a range oforientations with respect to the imaging module on a condition that thesecond optical radiation source of the second MI 120 and theretroreflector unit of the TGT 130, respectively, are within the fieldof view of the imaging module, i.e. that the second optical radiationsource of the second MI 120 and the retroreflector unit of the TGT 130,respectively, can be captured in an image by the imaging module.

Referring now to FIG. 4, there are shown schematic views of computerreadable digital storage mediums 400 a, 400 b according to exemplifyingembodiments of the present invention, comprising a DVD 400 a and afloppy disk 400 b. On each of the DVD 400 a and the floppy disk 400 bthere may be stored a computer program comprising computer code adaptedto perform, when executed in a processor unit, a method according toembodiments of the present invention such as have been described herein.

Although only two different types of computer-readable digital storagemediums have been described above with reference to FIG. 4, the presentinvention encompasses embodiments employing any other suitable type ofcomputer-readable digital storage medium, such as, but not limited to, anon-volatile memory, a hard disk drive, a CD, a Flash memory, magnetictape, a USB memory device, a Zip drive, etc.

Furthermore, the first MI typically comprises one or moremicro-processors (not shown in the drawings) or some other device withcomputing capabilities, e.g. an application specific integrated circuit(ASIC), a field programmable gate array (FPGA), a complex programmablelogic device (CPLD), etc., in order to perform various operations asdescribed herein. When performing steps of different embodiments of themethod of the present invention, the microprocessor typically executesappropriate software that is downloaded to the first MI and stored in asuitable storage area, such as for example a Random Access Memory (RAM),a Flash memory or a hard disk drive. Such a microprocessor or processingunit may alternatively or optionally be located externally relatively tothe first MI (and electrically connected to the first MI).

Referring now to FIGS. 5 a-5 b, there is shown a schematic flowchart ofa method 500 according to an exemplifying embodiment of the presentinvention.

The method 500 can determine position and orientation of a first MI. Thefirst MI comprises a retroreflector unit, at least one first opticalradiation source configured to emit optical radiation when activated,and at least one imaging module. A second MI, which comprises at leastone second optical radiation source configured to emit optical radiationwhen activated, and at least one reflective TGT, which comprises aretroreflector unit, are arranged in the vicinity of the first MI.

At step S501, angle and distance for the first MI and the at least oneTGT, respectively, are measured in relation to the second MI.

At step S502, the at least one imaging module is caused to captureimages, including alternating activation and deactivation of the atleast one first optical radiation source and the at least one secondoptical radiation source.

At step S503, an image representation of each captured image isproduced.

At step S504, differential images are created using the imagerepresentations.

At step S505, information regarding objects being present in thedifferential images is extracted.

Using the extracted information, the second MI and the at least one TGT,respectively, are distinguished from any other objects present in theimages at step S506.

On a condition that the second MI and the at least one TGT can bedistinguished from any other objects present in the images, steps S507and S508 are performed.

At step S507, any of said image representations is processed on basis ofsaid extracted information to determine angular information of thesecond MI and/or the at least one TGT with respect to at least one axis,respectively.

At step S508, orientation of the first MI is estimated on basis of angleand distance to the second MI and/or the at least one TGT, respectively,in relation to the first MI, and the angular information.

Optionally, steps S509-S513 may be performed.

At step S509, the position of the first MI and the position of the atleast one TGT are determined on basis of measured angle and distancerelatively to the first MI and the at least one TGT, respectively.

At step S510, distance between the first MI and the at least one TGT isdetermined on basis of the position of the first MI and the position ofthe at least one TGT.

At step S511, distance between the first MI and the at least one TGT isderived from the extracted information.

At step S512, distance between the first MI and the at least one TGT iscompared with distance between the first MI and the at least one TGT,derived from the extracted information.

At step S513, on basis of the comparison, the accuracy of thedistinguishing of the first MI and the at least one TGT, respectively,from any other objects present in the images is assessed.

In this manner, a procedure reducing or even eliminating false readings,i.e. inaccurately and/or incorrectly recognized targets and/or MIs, maybe achieved.

Optionally, compliance of the accuracy of the assessment performed instep S513 relatively to a predetermined accuracy criteria may bedetermined at step S514. In other words, a quality check of theassessment may be performed. A method for scanning a surface or a volumeof an object to determine appearance of the object with a first MI maycomprise transmitting optical radiation from the first MI to and receiveoptical radiation reflected from a position on the object in order tomeasure angle and distance to the position on the object. The directionof the transmitted optical radiation and/or the received opticalradiation is monitored by determining position and orientation of thefirst MI by consecutively performing a method such as been describedherein.

The transmitted optical radiation may be guided at predeterminedpositions over the object.

Prior to the scanning procedure, angle and distance to the one or moreTGTs from the second MI may be determined.

During the scanning procedure, angle and distance to the first MI fromthe second MI, angle between the first MI and the one or more TGTsrelatively to an axis, and/or angle between the first MI and and secondMI relatively to an axis may be determined repeatedly.

Although exemplary embodiments of the present invention have beendescribed herein, it should be apparent to those having ordinary skillin the art that a number of changes, modifications or alterations to theinvention as described herein may be made. Thus, the above descriptionof the various embodiments of the present invention and the accompanyingdrawings are to be regarded as non-limiting examples of the inventionand the scope of protection is defined by the appended claims. Anyreference signs in the claims should not be construed as limiting thescope.

1-39. (canceled)
 40. A method for determining orientation of a geodeticinstrument, said method comprising: causing at least one imaging moduleof the geodetic instrument to capture at least one image; producing animage representation of said at least one image; detecting in the imagerepresentation identifying means of a target and a measuring instrument;processing the image representation for determining angular informationof the measuring instrument and/or the target with respect to at leastone axis; receiving signals indicating distances and angles from themeasuring instrument to the geodetic instrument and to the target; andestimating orientation of the geodetic instrument based on said angleand distance to the measuring instrument and/or the target,respectively, in relation to the geodetic instrument, and the angularinformation.
 41. The method of claim 40, wherein processing the imagerepresentation comprises estimating at least one angle between themeasuring instrument and the at least one target with respect to the atleast one axis, wherein the angular information includes the estimatedat least one angle.
 42. The method of claim 40, wherein processing theimage representation comprises estimating at least one angle bydetermining, on the image representation, a distance between themeasuring instrument and the at least one target, a distance between themeasuring instrument and the at least one axis and/or a distance betweenthe at least one target and the at least one axis.
 43. The method ofclaim 42, wherein determination of a distance comprises determining inthe captured image a number of pixels between the measuring instrumentand the at least one target, between the measuring instrument and the atleast one axis, and/or between the at least one target and the at leastone axis, wherein a dimension of a pixel in the image corresponds to apredetermined distance.
 44. The method of claim 40, wherein the angularinformation includes a first angle obtained by determining in the imagerepresentation a distance between the measuring instrument and a firstaxis, a second angle obtained by determining in the image representationa distance between the measuring instrument and a second axis and athird angle defined by the first axis and a line intersecting themeasuring instrument and the at least one target.
 45. The method ofclaim 40, further comprising alternating activation and deactivation ofa first radiation source of the geodetic instrument and of a secondradiation source of the measuring instrument for creating differentialimages using image representations produced from images captured atdifferent points in time, the identifying means of the target and themeasuring instrument being detected using the created differentialimages.
 46. The method of claim 40, wherein the geodetic instrument is aportable geodetic scanner and the measuring instrument is a totalstation.
 47. A computer program product or a computer-readable digitalstorage medium comprising a computer program product, said computerprogram product comprising computer-executable components for performinga method according to claim 40 when the computer-executable componentsare executed on a processing unit.
 48. A geodetic instrument comprising:a communication module adapted to receive signals from a measuringinstrument, said received signals indicating distances and angles fromsaid measuring instrument to the geodetic instrument and to a target; atleast one imaging module adapted to capture at least one image andproduce an image representation of said at least one image; a controlmodule adapted to cause the at least one imaging module to capture atleast one image; and a processing module adapted to: detect in the imagerepresentation identifying means of the target and said measuringinstrument; process the image representation for determining angularinformation of said measuring instrument and/or the target with respectto at least one axis; and estimate orientation of the geodeticinstrument based on said angle and distance to the measuring instrumentand/or the target, respectively, in relation to the geodetic instrument,and the angular information.
 49. The geodetic instrument of claim 48,wherein the processing module is adapted to estimate an angle betweensaid measuring instrument and the at least one target with respect tothe at least one axis, the angular information comprising the estimatedangle.
 50. The geodetic instrument of claim 48, wherein the processingmodule is adapted to estimate at least one angle by determining adistance between said measuring instrument and the at least one target,a distance between said measuring instrument and the at least one axisand/or a distance between the at least one target and the at least oneaxis, the angular information comprising the estimated angle.
 51. Thegeodetic instrument of claim 50, wherein the processing module isadapted to determine a distance by determining in the captured image anumber of pixels between the measuring instrument and the at least onetarget, between said measuring instrument and the at least one axis,and/or between the at least one target and the at least one axis,wherein a dimension of a pixel in the image corresponds to apredetermined distance.
 52. The geodetic instrument of claim 48, furthercomprising at least one first radiation source, wherein the controlmodule is adapted to selectively activate and deactivate the at leastone first radiation source and to cause the communication module to sendcontrol signals instructing activation or deactivation of at least onesecond radiation source at said measuring instrument, said processingmodule being adapted to create differential images using imagerepresentations produced by the at least one imaging module at differentpoints in time, the identifying means of the target and said measuringinstrument being detected using the created differential images.
 53. Thegeodetic instrument of claim 48, wherein the angular informationincludes a first angle obtained by determining in the imagerepresentation a distance between the measuring instrument and a firstaxis, a second angle obtained by determining in the image representationa distance between the measuring instrument and a second axis and athird angle defined by the first axis and a line intersecting themeasuring instrument and the at least one target.
 54. The geodeticinstrument of claim 48, being a portable geodetic scanner.